Blow-by gas including unburnt gas generated at an engine includes moisture. For example, in a case where the engine stops in a cold district, the moisture of the blow-by gas remaining inside a PCV valve may freeze. Thus, technique related to a measure against the freezing of the PCV valve includes technique, for example, presented in Patent document 1, wherein a freeze detection portion detecting presence/absence of the freezing of the PCV valve and a freeze release portion releasing the freezing of the PCV valve are described.
That is, in Patent document 1, a blow-by gas recirculation apparatus which sends the blow-by gas to a surge tank for air-intake via the PCV valve provided at a head cover is configured. A thermal heater is provided at a position of an outer circumference of the PCV valve, and the thermal heater is electrified in a case where the freeze detection portion detects that “freezing is present”, and thus the freezing is released.
In addition, Patent document 2 presents a configuration where a heating pipe is fixedly attached to an outer circumference of a PCV passage so that the freezing at a union at an intake manifold-side at the PCV passage is released, although it is not a configuration which releases the freezing of the PCV valve. According to Patent document 2, a high-temperature coolant water heated at an engine is supplied to the heating pipe, and thus the freezing within the PCV passage is removed.